The production of sophisticated devices therefore should not be considered to be a possible activity for a fly-by-night terrorist group. It is, however, conceivable in the context of a nationally supported program able to provide the necessary resources and facilities and an established working place over the time required. It could be further imagined that under the sponsorship of some malevolent regime, a team schooled and prepared in such a setting could be dispatched anywhere to acquire material and produce a device. In such a case, although the needs of the preparation program might have been met, the terrorists would still have to obtain and set up the equipment needed for the reduction to metal and its subsequent handling and to spend the time necessary to go through those operations.

BUILDING A NUCLEAR DEVICE WOULD TAKE A VERY LONG TIME AND EVEN THEN THERE IS NO GUARANTEE IT WOULD WORK

The fundamental question, however, would still remain: that of whether the object designed and built would or would not actually behave as pre dicted. Even with their tremendous experience, the weapons laboratoriesfind on occasion that their efforts are flawed. Admittedly, weapons designers are now striving to impose refinements on an already highly refined product, but they have had to digest surprises and disappointments at many points along the way.

For persons new to this business, as it may be supposed a terrorist group is, there is a great deal to learn before they could entertain any confidence that some small, sophisticated device they might build would perform as desired. To build the device would require a long course of study and a long course of hydrodynamic experimentation. To achieve the size and weight of a modern weapon while maintaining performance and confidence in perfor mance would require one or more full-scale nuclear tests, although consid erable progress in that direction could be made on the basis of nonnuclear experiments.

STEALING A SMALL AMOUNT OF FISSILE MATERIAL DOES NOT MEAN A SMALL NUCLEAR DEVICE CAN BE BUILT

Merely on the basis of the fact that sophisticated devices are known to be feasible, it cannot be asserted that by stealing only a small amount of fissile material a terrorist would be able to produce a device with a reliable multikiloton yield in such a small size and weight as to be easy to transport and conceal. Such an assertion ignores at least a significant fraction of the problems that weapons laboratories have had to face and resolve over the past forty years. It is relevant to recall that today's impressively tidy weapons came about only at the end of a long series of tests that provided the basis for proceeding further. For some of these steps, full-scale nuclear tests were essential. In retrospect, not every incremental step taken would now seem necessary. Indeed, knowing only that much smaller and lighter weapons are feasible, it is possible at least to imagine going straight from the state of understanding in 1945 to a project to build a greatly improved device. The mere fact of knowing it is possible, even without knowing exactly how, would focus terrorists' attention and efforts.

Two options for nuclear devices to be built by terrorists are considered here: that of using the earliest design principles in a so-called crude design and that of using more advanced principles in a so-called sophisticated design.

A crude design is one in which either of the methods successfully dem onstrated in 1945---the gun type and the implosion type---is applied. In the gun type, a subcritical piece of fissile material (the projectile) is fired rapidly into another subcritical piece (the target) such that the final assembly is supercritical without a change in the density of the material. In the implosion type, a near-critical piece of fissile material is compressed by a converging shock wave resulting from the detonation of a surrounding layer of high explosive and becomes supercritical because of its increase in density.

A small, sophisticated design is one with a diameter of about 1 or 2 feet and a weight of one hundred to a few hundred pounds, so that it is readily transportable (for example, in the trunk of a standard car). Its size and weight may be compared with that of a crude design, which would be on the order of a ton or more and require a larger vehicle. It would also be possible, in about the same size and weight as a crude model but using a more sophis ticated design, to build a device requiring a smaller amount of fissile material to achieve similar effects.

The terrorists would need something like a critical mass of the material they propose to use. For a particular fissile material, the amount that con stitutes a critical mass can vary widely depending on its density, the char acteristics (thickness and material) of the reflector employed, and the nature and fractional quantity of any inert diluents present (such as the oxygen in uranium oxide, the uranium 238 in partially enriched uranium 235, or chem ical impurities).

As a final general observation, for a crude design, terrorists would need something like 5 or 6 kg of plutonium or 25 kg of very highly enriched uranium (and more for a gun-type device), even if they planned to use metal. They would have to acquire more material than is to go into the device, since with metal considerably more material is required to work with than will appear in the finished pieces.

CRUDE NUCLEAR DEVICES WOULD DEMAND HUGE AMOUNTS OF FISSILE MATERIAL AND WOULD WEIGH MORE THAN A TON

In sum, several conclusions concerning crude devices based on early design principles can be made.

I . Such a device could be constructed by a group not previously engaged in designing or building nuclear weapons, providing a number of requirements were adequately met.

2. Successful execution would require the efforts of a team having knowledge and skills additional to those usually associated with a group engaged in hijacking a transport or conducting a raid on a plant.

3. To achieve rapid turnaround (that is, the device would be ready within a day or so after obtaining the material), careful preparations extending over a considerable period would have to have been carried out, and the materials acquired would have to be in the form prepared for.

4. The amounts of fissile material necessary would tend to be large--- certainly several, and possibly ten times, the so-called formula quantities.

5. The weight of the complete device would also be large---not as large as the first atomic weapons (~10,000 pounds), since these required aero dynamic cases to enable them to be handled as bombs, but probably more than a ton.